Measurement of the speed of sound in human cortical bone in vivo has been made and the results validated. Measurement also of bone mineral content in the radius has been made by the Cameron Sorenson method and measurement of bone mineral density in the femur will be attempted, using the ratio of coherent to Compton scattered photons, the in vitro testing having been done. These measurements provide a new approach to the problem of measuring the physical characteristics of bone. The speed of sound and the density measurements combined enable an assessment of the elasticity of bone to be made for the first time. This new combined method has been used to investigate patients with osteoporosis, metabolic osteodystrophy and hip and knee joint arthritis before total joint prothesis surgery.